1. Field of the Invention
The present invention relates to a digital image watermarking apparatus and method, and more specifically, to a digital image watermarking apparatus and method which are able to extract the embedded watermark, and simultaneously not deteriorate the quality of a digital image, and which are able to extract the watermark without an original image by leaving a watermark in spite of print or various image alterations.
2. Description of the Related Art
As creation and distribution of-digital media, such a still image as a picture image or such a moving picture as an animation increase, the digital media is circulated through various storage media or network, and thus illegal copy or illegal alteration is largely increased. Various devices have been developed to prevent the digital media from illegally being altered or copied or circulated. As a device for implementing such object, the inventor of the present invention paid attention to a digital watermarking technology.
The digital watermarking technology is to prevent copy, distribution, alteration, sale, etc. without permission of the ownership holder of the digital data works by additionally embedding information undistinguishable with the naked eye in the digital data works.
There are a spatial domain method, a frequency domain method, a spread spectrum communication method, etc. in the digital watermarking technology widely known up to now. These digital watermarking technologies have some advantages in that it is easy to embed a watermark (spatial domain method) and it is difficult to remove a watermark (frequency domain method), etc., whereas, they have various disadvantages in that it is weak in an operation like filtering (spatial domain method), an image is damaged according to the value of coefficient (frequency domain method), or an original image is necessary for extracting a watermark and an original image is largely altered by an embedding watermark (spread spectrum communication method).
That is, the conventional digital watermarking technologies as described above failed to meet all the requirements, in particular, i) it must be difficult or impossible to remove the watermark embedded in a digital image (difficulty of access); ii) even if the digital image is printed or an image alteration for printing, for example, dithering or halftone, is made, the watermark embedded in the digital image must be robust enough to be extracted after such print or image alteration (robustness against alteration): iii) when a watermark is embedded in the digital image, the deterioration of quality of the digital image by watermark must be minimized (conservation of quality of the digital image); and iv) the embedded watermark can not be known except by a copyright holder or a person whose use is allowed (hiding of the embedded information) to prevent the illegal alteration, copy and distribution of the digital media thereby its range of application is very restrictive and it is difficult to fully obtain the object described above.